Competition-based detection assays

ABSTRACT

Disclosed herein are methods and kits which are useful for detecting presence of an enzyme and the relative amount of glycan associated with the enzyme in a test sample based upon the enzyme&#39;s ability to competitively inhibit the binding of a ligand in such test sample. The present invention provides the ability to evaluate cell culture conditions and optimize the desired glycoform content of recombinantly prepared enzymes.

RELATED APPLICATION(S)

This application claims the benefit of U.S. Provisional Application No. 61/494,643, filed Jun. 8, 2011 (Attorney Docket No. SHIR-024-001). The entire teachings of the above application are incorporated herein by reference.

BACKGROUND OF THE INVENTION

Glycoproteins and glycoenzymes are proteins that contain a post-translational modification wherein oligosaccharide chains (known as glycans) are covalently attached to the protein's or enzyme's polypeptide side chains. This process, which is known as glycosylation, is one of the most abundant protein post-translational modifications. It is estimated that more than half of all cellular and secretory proteins are glycosylated. (Apweiler et al., 1999, Biochim. Biophys. Acta 1473: 4-8). Although mammalian glycoprotein oligosaccharides, for example, are constructed from a limited number of monosaccharides, their structural diversity is vast due to complex branching patterns. Glycoproteins, therefore, represent a diverse group of modifications, and variants of glycoproteins or glycoenzymes (which are known as glycoforms) can impact protein or enzyme activity or function. The ability to evaluate and distinguish specific glycan structures during the preparation of recombinant enzymes can accordingly provide valuable information relating to recombinant enzyme development and further optimization of the desired glycoform content of such recombinant enzymes.

Conventional techniques which are routinely employed for glycoprotein and glycoenzyme analysis include mass spectrometry, lectin affinity chromatography and western blotting. Although these conventional methods of analysis are generally accurate, they are time consuming, require purification of the protein, and some, such as mass spectrometry, require specific expertise and are technically challenging. (Wang et al., 2006, Glycobiol. Epub.; Qiu et al., 2005, Anal. Chem. 77:2802-2809; Qiu et al., 2005, Anal Chem. 77:7225-7231; Novotny et al., 2005, J. Sep. Sci. 28:1956-1968). Accordingly, these issues make the routine use of such technologies impractical for high-throughput monitoring of enzyme glycosylation, especially during process development and manufacturing. Such technologies may also present challenges to a typical research laboratory attempting to study the impact of glycosylation on the biological properties of proteins and enzymes.

Traditionally, to provide a quantitative assessment of the glycan structure of a glycoprotein, lectin array platforms required the use of either a reliable glycoprotein-specific antibody or direct conjugation of a fluorescent dye to the glycoprotein. These antibody-based detection strategies are limited by the fact that antibody recognition of a given glycoprotein or glycoenzyme may be blocked or reduced depending on the type of glycan structure linked to the protein or enzyme, thereby allowing recognition of only a subset of the total glycoprotein pool and not the range of potential glycan structures. Antibody-based recognition may also require multiple binding and wash steps, which can add time and complexity to an analysis. While these problems can be circumvented using direct labeling of the glycoprotein, direct labeling remains limited to pure preparations of material, since the labeling techniques do not discriminate among proteins. Accordingly, direct labeling cannot be used for “dirty” or in-process samples. The utility of currently available methods for glycan analysis may be further limited because large quantities of highly purified materials may not readily be available from in-process test samples. Furthermore, purified material may only represent a subset of the initial glycoform population because the purification process is typically selective for certain glycan structures.

The identification and characterization of protein and enzyme glycoforms is essential in the development of recombinant proteins and enzymes. For example, glycosylation of recombinantly-prepared enzymes must frequently be controlled during production to maintain the efficacy and safety of such recombinant enzymes, and cell culture conditions can affect the carbohydrate structures of glycoproteins. Further understanding of cell culture conditions that can impact the carbohydrate structures of recombinantly-prepared proteins or enzymes is also important for the development of an effective and robust recombinant production process.

Improved methods and compositions are needed for the rapid, direct and systematic identification and evaluation of the glycan structures of a given protein or enzyme and their variant glycoforms. High throughput methods and compositions that are capable of efficiently assessing and distinguishing among a diverse range of glycosylation states or glycoforms, as well as determining the relative differences in the amount of glycans associated with such glycosylation states or glycoforms, would provide valuable information for drug discovery and disease therapeutics, provide valuable tools regarding ongoing research, and facilitate the optimization of recombinant production processes.

SUMMARY OF THE INVENTION

The present invention provides novel methods, assays and compositions for the accurate and rapid identification and/or detection of various glycoforms of enzymes and the relative amount of glycan associated with such glycoforms. In particular, the present invention relies upon the ability of an enzyme of interest to competitively inhibit the binding of a ligand to detect such enzyme's presence in a test sample, as well as to determine the relative amount of glycan associated with such enzyme. The methods, assays and compositions disclosed herein also provide novel strategies for analyzing the different glycoforms of unpurified proteins or enzymes in cell culture harvest test samples. The methods, assays and compositions disclosed herein also provide novel strategies for analyzing the relative amounts of glycan associated with such different glycoforms. Furthermore, the present invention provides the ability to detect and distinguish among different glycoforms or glycovariants of an enzyme in upstream harvest test samples, thereby facilitating the optimization of cell culture conditions that affect the viable glycoform content of recombinantly-prepared enzymes. Even further, the present invention provides the ability to detect and distinguish among the relative amount of glycan associated with various glycoforms or glycovariants of an enzyme in upstream harvest test samples, thereby further facilitating the optimization of cell culture conditions that affect the viable glycoform content of recombinantly-prepared enzymes. The methods and kits of the present invention are advantageously capable of determining the presence of glycosylated enzymes in a test sample, as well as determining the relative amount of glycan associated with those glycosylated enzymes, irrespective of the presence of additional cellular proteins, biological materials or other contaminants which may be present in that test sample.

Disclosed herein are methods for detecting the presence of an enzyme (e.g., a recombinantly prepared enzyme) and the relative amount of glycan associated with the enzyme in a test sample, such methods comprising contacting the test sample with at least one capture agent (e.g., a lectin) under conditions appropriate for binding of glycosylated enzyme in the test sample to the capture agent, wherein upon binding of glycosylated enzyme to capture agent a complex is formed which is referred to herein as a “bound enzyme.” Some embodiments also contemplate separation of the test sample from the bound enzyme produced by the previous step (e.g., using routine means such as washing) followed by detection of the extent to which the bound enzyme inhibits binding of a ligand to the capture agent. The extent to which the bound enzyme inhibits binding of the ligand to the capture agent is indicative of the relative amount of glycan associated with the enzyme in the test sample.

Also disclosed are methods for detecting the presence of an enzyme (e.g., a recombinantly prepared enzyme) and the relative amount of glycan associated with the enzyme in a test sample, wherein such methods comprise the steps of contacting a test sample with at least one capture agent (e.g., a lectin) under conditions appropriate for binding of the glycosylated enzyme, and thereby forming a bound enzyme when glycosylated enzyme is present. The methods of the present invention also contemplate separating the bound enzyme from the test sample and contacting the bound enzyme with at least one ligand for the capture agent. In accordance with the present invention, the extent to which such bound enzyme competitively inhibits binding of the at least one ligand to the capture agent is indicative of the relative amount of glycan associated with the glycosylated enzyme of interest in the test sample. Conversely, the absence of competitive inhibition is indicative of the absence of the glycosylated enzyme of interest in the test sample. The methods disclosed herein provide the ability to optimize the desired glycoform content of one or more recombinant enzymes during recombinant preparation.

In one embodiment, the methods of the present invention further comprise the step of fixing a capture agent (e.g., one or more lectins) onto a solid support (e.g., a microtiter plate or one or more populations of beads). In one embodiment, such solid support may comprise or be coated with avidin, streptavidin or a metal chelator such as a nickel chelate. If such solid support comprises avidin or streptavidin, the use of derivatized lectins (e.g., biotinylated lectins) are preferred. If such solid support comprises a nickel chelate, the use of six consecutive histidine residues (6His) as an affinity tag is preferred. For example, a capture agent may be a fusion protein which includes one or more histidine (HIS) residues (e.g., at least one, at least two, at least three, at least four, at least five, at least six, at least eight, at least ten, at least twelve, at least twenty, at least twenty five or more HIS residues) at either the N- or C-terminus as an affinity tag to facilitate fixing of that capture agent (i.e., the fusion protein) to a solid support.

In one embodiment of the present invention the capture agent comprises one or more lectins. The lectins contemplated by the methods, assays and kits of the present invention include, for example, concanavalin A, wheat germ agglutinin, Jacalin, lentil lectin, peanut lectin, lens culinaris agglutinin, Griffonia (Bandeiraea) simplicifolia lectin II, Aleuria aurantia lectin, hippeastrum hybrid lectin, sambucus nigra lectin, maackia amurensis lectin II, ulex europaeus agglutinin I, lotus tetragonolobus lectin, galanthus nivalis lectin, euonymus europaeus lectin, ricinus communis agglutinin I, and any combinations thereof.

In another embodiment of the present invention the capture agent comprises a receptor, or a binding fragment thereof, known to demonstrate affinity for or otherwise bind to one or more particular glycoforms of an enzyme. For example, mannose-6-phosphate (M6P) binds the mannose-6-phosphate receptor (M6PR), and in one embodiment a recombinant fusion protein comprising the M6PR or a binding domain thereof (e.g., M6PR domain 9) may serve as the capture agent. In one embodiment, the recombinant fusion protein capture agent may also comprise one or more histidine residues (e.g., 6His) to facilitate purification, capture and/or fixing of the capture agent to a solid support. In one embodiment of the present invention, the capture agent comprises the fusion protein M6PR(D9)6His.

Also disclosed is a method of determining the intrinsic enzymatic activity of the ligand bound to the capture agent by contacting such ligand with a substrate, for example, a substrate which has known reactivity with the ligand. In accordance with the methods of the present invention, the presence of intrinsic enzymatic activity is indicative of the presence of ligand bound to the capture agent. Alternatively, the absence of intrinsic enzymatic activity may be indicative of the absence of such ligand bound to the capture agent in the test sample.

In one embodiment, the methods, assays and kits of the present invention contemplate determining intrinsic enzymatic activity by contacting ligand bound capture agent with a substrate which is known to predictably react with the ligand of interest. For example, if the ligand is agalsidase alfa the selected substrate may be 4-nitrophenyl-α-D-galactopyranoside, if the ligand is galactocerebrosidase the selected substrate may be 4-nitrophenyl-β-D-galactopyranoside, and if the ligand is aryl sulfatase A the selected substrate may be p-nitrocatechol sulfate. The presence or absence of intrinsic enzymatic activity of the bound ligand may be determined by means which are known to those of ordinary skill in the art. In one embodiment a quantitative assessment of the conversion of substrate to product may be indicative of intrinsic enzymatic activity of the ligand. For example, in one embodiment, following contacting an enzyme (e.g., ligand) with a substrate, a relative increase in the formation of a product, or the conversion of substrate to product, in each case of about 5%, 10%, 20%, 30%, 40%, 50% or more, or preferably about 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 99%, 100% or more, may be indicative of intrinsic enzymatic activity of the ligand. Substrates contemplated by the present invention include, for example, 4-nitrophenyl-α-D-galactopyranoside, 4-nitrophenyl-β-D-galactopyranoside and para-nitrocatechol sulfate.

Also disclosed herein are kits which are useful for detecting the presence of glycosylated enzymes (e.g., a recombinantly prepared glycosylated enzyme) and the relative amount of glycan associated with the glycosylated enzymes in a test sample. Such kits comprise at least one capture agent (e.g., a lectin) capable of binding a glycosylated enzyme, and at least one ligand which is competitive with such glycosylated enzyme for binding the capture agent. In one embodiment the kits of the present invention comprise a solid support (e.g., a multiple well microtiter plate), onto which may be fixed a capture agent (e.g., the lectin sambucus nigra agglutinin).

In one embodiment, the kits of the present invention comprise a capture agent which is known to bind or demonstrate affinity for the targeted glycoform of the enzyme of interest (e.g., the M6PR(D9)6His fusion protein), and a ligand which is known to compete with such enzyme for binding to the capture agent. In one embodiment, such kits may also comprise a means of separating or removing excess test sample from the solid support, for example by washing, or other routine means available to one of ordinary skill in the art.

Also contemplated are kits which are capable of identifying multiple glycosylated enzymes and multiple glycoforms of those enzymes in the same test sample. For example, the kits of the present invention may comprise multiple capture agents (e.g., lectins) fixed onto one or more solid supports (e.g., populations of inert beads), and thus provide the capability of binding to multiple glycoforms of one or more enzymes in the same test sample. The kits of the present invention may also comprise one or more ligands (each of which compete with a particular enzyme whose presence is suspected in a test sample for binding to the one or more capture agents) to determine the extent to which such enzymes competitively inhibit binding of the ligands to the capture agents. Preferably, the selected ligand is known to predictably bind to, or react with, the selected capture agent, and in particular, to compete with the enzyme of interest for binding the capture agent. For example, if the enzyme is idursulfase the selected ligand may be agalsidase alfa, if the enzyme is heparan N-sulfatase the selected ligand may be agalsidase alfa, if the enzyme is aryl sulfatase A the selected ligand may be agalsidase alfa. Based upon the binding specificity or reactivity of the test sample with the ligand, one having ordinary skill in the art may use routine means to assess the extent to which the enzyme competitively inhibits the binding of the ligand to the capture agent (e.g., by detecting the presence or absence of intrinsic enzymatic activity of the ligand bound to the capture agent, e.g., by contacting the ligand bound to the capture agent with a substrate known to react with the ligand, e.g., by quantitatively determining the conversion of substrate to product).

The above discussed and many other features and attendant advantages of the present invention will become better understood by reference to the following detailed description of the invention when taken in conjunction with the accompanying examples.

BRIEF DESCRIPTION OF THE DRAWINGS

The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawings will be provided by the Office upon request and payment of the necessary fee.

FIG. 1 schematically illustrates one embodiment of the present invention in which biotinylated lectins are bound to streptavidin-coated plates, to which are added test sample materials containing different preparations of a given glycosylated enzyme which are allowed to bind. Unbound test sample materials are then removed by a wash step, and specific detection of the bound enzyme is performed by the addition of the appropriate substrate and assay conditions.

FIG. 2 illustrates binding of agalsidase alfa to immobilized wheat germ agglutinin (WGA) and concanavalin A (ConA) as determined by measuring the enzymatic activity of agalsidase alfa (Replagal®) based on the substrate 4-nitrophenyl-α-D-galactopyranoside.

FIG. 3 illustrates binding of galactocerebrosidase (GalC) to immobilized wheat germ agglutinin (WGA), concanavalin A (ConA), and Sambucus nigra lectin (SNA) as determined by measuring enzymatic activity of GalC using the substrate 4-nitrophenyl-β-D-galactopyranoside.

FIG. 4 illustrates binding of galactocerebrosidase (GalC) treated with increasing concentrations of sialidase to immobilized Sambucus nigra lectin (SNA), as determined by measuring enzymatic activity of GalC using the substrate 4-nitrophenyl-β-D-galactopyranoside.

FIG. 5 illustrates linkage-specific binding of purified aryl sulfatase A (ARSA) containing sialic acid in either α-2, 6 or α-2, 3 linkages to Sambucus nigra lectin (SNA), as determined by measuring enzymatic activity of ARSA using the substrate p-nitrocatechol sulfate.

FIG. 6 illustrates binding of galactocerebrosidase (GalC) cell culture from different harvest test samples to Sambucus nigra lectin (SNA), as determined by measuring enzymatic activity of GalC using the substrate 4-nitrophenyl-β-D-galactopyranoside.

FIG. 7 schematically illustrates one embodiment of the present invention in which the M6PR(D9)6His fusion protein is bound to a nickel chelate-coated 96-well plate, to which are added test samples containing different preparations of a given glycosylated enzyme which are allowed to bind. Unbound test sample material is then removed by a wash step, and specific detection of the bound enzyme is performed by the addition of the appropriate substrate and assay conditions.

FIG. 8 illustrates detection differences in the amount of aryl sulfatase A (ARSA) associated M6P using ARSA lots with known amounts of M6P.

FIG. 9 illustrates detection differences in the relative amounts of sialic acid associated with idursulfase, heparan N-sulfatase (HNS), and ARSA using agalsidase alfa lots with known amounts of sialic acid.

FIG. 10 illustrates detection differences in the relative amounts of M6P associated with idursulfase, HNS, and ARSA using agalsidase alfa lots with known amounts of M6P.

DETAILED DESCRIPTION OF THE INVENTION

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. In addition, the materials, methods, and examples are illustrative only and are not intended to be limiting.

Disclosed herein are high throughput methods, assays, kits and compositions for screening complex test samples for the presence of glycosylated enzymes of interest or for determining changes in glycosylation of such enzymes. Also disclosed herein are methods and kits which are capable of detecting the intrinsic activity of an enzyme in a test sample as a means of determining the presence of that enzyme in the test sample. For example, in one aspect the present invention relies upon the intrinsic enzymatic activity of an enzyme to detect its presence in a test sample. This is in contrast to antibody-based detection schemes which can be negatively influenced by changes in glycosylation, for example by hindrance of antibody recognition of the enzyme. Also disclosed herein are methods and kits which are capable of determining the relative differences in the amount of glycan associated with glycosylated enzymes present in complex test samples. For example, in another aspect the present invention relies upon the intrinsic ability of an enzyme to competitively inhibit binding of a ligand to a capture agent to detect the extent to which the enzyme inhibits binding of the ligand to the capture agent. Without wishing to be bound by theory, it is believed that the relative amount of glycan associated with a glycosylated enzyme of interest correlates to the extent to which the glycosylated enzyme inhibits binding of the ligand to the capture agent. Specifically, the present invention relates to the discovery that the intrinsic ability of an enzyme to competitively inhibit binding of a ligand with demonstrated affinity and specificity for binding to a capture agent is consistent with the relative amount of glycan associated with the glycosylated enzyme. The invention provides the ability to study cell culture conditions and optimize the desired glycoform content of biological samples, and in particular of recombinantly prepared enzymes.

In the context of the present invention, the term “glycan” refers to the carbohydrate portion of a glycoprotein or glycoenzyme. Generally, glycans tend to be oligosaccharides or polysaccharides. The terms “glycoform” and “glycovariant” refer to an isoform of a protein or enzyme with a unique primary, secondary, tertiary, and/or quaternary structure based upon the number and/or structure of the glycans attached to such protein or enzyme. It is often the case that a single glycoprotein may have over a thousand different glycoforms or glycovariants, all of which are based on differences in the glycan portion or glycosylation pattern of the glycoprotein. The term “glycosylation” refers to the process or result of adding saccharides to proteins and thus forming “glycoproteins”. Glycosylation includes both N-linked glycosylation to the amide nitrogen of asparagine side chains, and O-linked glycosylation to the hydroxy oxygen of serine and threonine side chains.

The term “test sample” is used in its broadest sense and means any preparation, preferably obtained from biological media or materials, including biologically or recombinantly derived media which may contain, among other things, naturally occurring or recombinantly prepared peptides, polypeptides or proteins, enzymes, lipid or carbohydrate molecules, or glycosylated proteins or enzymes, or other samples obtained from a recombinant media, including any fractions thereof. The test samples contemplated by the present invention are preferably obtained from in-process or “dirty” biological systems, for example, those obtained during the preparation of a recombinant enzyme.

As used herein, the term “solid support” refers to any material that provides a solid or semi-solid structure with or upon which another material can be attached or fixed. Such materials include smooth supports (e.g., metal, glass, plastic, silicon, and ceramic surfaces) as well as textured and porous materials. Such materials also include, but are not limited to, gels, rubbers, polymers, dendrimers and other non-rigid materials. Solid supports need not be flat. Supports include any type of shape including spherical shapes (e.g., beads) and may include multiple well microtiter plates, and may optionally be coated with proteins, resins or other similar reagents, such as for example, avidin, streptavidin, metal ions or chelates (e.g., a nickel chelate).

The present invention contemplates the use of one or more capture agents to facilitate capture, immobilization or fixing of the glycosylated enzyme of interest (e.g., capture or fixing of one or more glycosylated enzymes onto a solid support). As used herein, the phrase “capture agent” refers to a compound or a material which demonstrates affinity for or is capable of conjugating or associating with one or more specific saccharide or carbohydrate moieties. Preferably the selected capture agent demonstrates specific or discriminatory affinity for one saccharide moiety, such that the capture agent will only bind one particular glycoform of a given enzyme. In a preferred embodiment of the present invention, the capture agent is selected based upon its specific affinity to one or more glycan structures. When contacted with such a glycan structure or glycosylated enzyme in accordance with the present invention the capture agent will form a complex referred to herein as a “bound enzyme.”

In one embodiment of the present invention, the capture agent is a lectin. Lectins represent a family of saccharide-recognizing proteins which are classified based upon the specificity of the mono-saccharide groups for which they exhibit the highest affinities. Lectins are non-enzymatic and non-immune in nature and are capable of binding to the saccharide moiety of a glycoprotein or glycoenzyme. As used herein, the term “lectin” refers to a non-antibody compound which binds to a specific carbohydrate structure or target, such as for example, a glycosylated biological or recombinantly derived molecule or a glycosylated enzyme, to form a larger complex. When used in accordance with the present invention, one or more lectins are selected based upon such lectins' affinity for a specific glycan structure or a glycosylated enzyme. Preferably, the lectin is selected for its biological affinity for a specific glycan structure, or for a targeted glycosylated enzyme of interest whose presence is suspected in a test sample. In a preferred embodiment the methods and kits of the present invention contemplate the selection of lectins which are capable of recognizing and discriminatorily binding to specific glycoforms of an enzyme. For example, if the enzyme of interest in a selected test sample is a glycosylated form of the enzyme agalsidase alpha, then a lectin with affinity for that enzyme (such as, for example, the lectin concanavalin A) would be preferentially incorporated into the assays, kits and methods of the present invention. By way of further example, if the enzyme of interest in a selected test sample is a glycosylated form of the enzyme idursulfase, then a lectin with affinity for that enzyme (such as, for example, SNA Lectin) would be preferentially incorporated into the assays, kits and methods of the present invention.

The lectin's biological affinity for a specific glycan structure can be exploited in accordance with the present invention to isolate glycosylated enzymes or specific glycoforms of an enzyme in a test sample. Numerous lectins are commercially available, and information on the binding specificity of a given lectin can be obtained from the manufacturer or as is described herein. Representative lectins include, but are not limited to, concanavalin A (Con A), wheat germ agglutinin (WGA), Jacalin, lentil lectin (LCA), peanut lectin (PNA), Lens culinaris agglutinin (LCA), Griffonia (Bandeiraea) simplicifolia lectin II (GSLII) Aleuria aurantia Lectin (AAL), Hippeastrum hybrid lectin (HHL, AL), Sambucus nigra lectin (SNA), Maackia amurensis lectin II (MAL II), Ulex europaeus agglutinin I (UEA I), Lotus tetragonolobus lectin (LTL), Galanthus nivalis lectin (GNL), Euonymus europaeus lectin (EEL), Ricinus communis agglutinin I (RCA), or combinations thereof.

In an alternative embodiment of the present invention, the capture agent may comprise one or more fusion proteins, wherein such fusion proteins preferably comprise one or more binding domains which are capable of recognizing and binding to one or more specific saccharide or carbohydrate moieties of a glycosylated enzyme. For example the mannose-6-phosphate receptor (M6PR) is capable of binding mannose-6-phosphate (M6P). The M6PR is approximately 300 kDa and consists of approximately 15 extracellular domains. In one embodiment of the invention a fusion protein capture agent comprises one or more M6PR binding domains (e.g., M6PR domains 1, 3, 5, 9 and/or 11) which demonstrate affinity for M6P and/or other glycoforms of interest. Preferably, the selected binding domain demonstrates high affinity for the saccharide or carbohydrate moieties of interest (e.g., M6PR domains 3 and 9 correspond to high affinity M6P binding sites). The recombinant fusion protein capture agents of the present invention may optionally comprise one or more regions or tags to facilitate purification, isolation or fixation of the capture agent (e.g., fixation to a solid support). For example, in one embodiment of the present invention six histidine residues (6His) may be linked to a M6PR binding domain to facilitate the purification, capture or fixation of the capture agent to a solid support (e.g., a nickel chelate-coated 96-well plate). The fusion protein capture agents of the present invention may further comprise one or more linker or spacer groups. In one embodiment of the present invention, the capture agent comprises the fusion protein M6PR(D9)6His which may be expressed, for example, in HT1080 cells and purified using nickel chelate affinity chromatography.

The present invention contemplates that capture agents (e.g., lectins) may optionally be fixed onto any portion of a solid support (e.g., may be attached to an interior portion of a porous solid support material). As used herein, the terms “fixed”, “affixed” and “fixing” mean bound, adhered to or immobilized, for example, physically and/or chemically. As the term specifically relates to a solid support and a capture agent, “fixed” or “affixed” mean that the capture agent remains bound to, or immobilized on, a solid support despite being subjected to wash conditions or conditions which may alter such physical or chemical bonds. Fixing may be, for example, spontaneous or result from an additional step. Exemplary methods of fixing include evaporation (for example, removal of volatile solvent), cooling (for example, resulting in a phase change from liquid to solid, or viscosity thickening), and curing (for example, polymerization and/or crosslinking). The present invention contemplates the use of derivatized lectins as capture agents to enhance the ability to fix a lectin onto a solid support. For example, biotinylated lectins demonstrate an enhanced ability to affix onto a solid support coated with avidin or streptavidin, (e.g., a 96 well plate, optionally coated with avidin or streptavidin) and the use of such derivatized lectins are contemplated by the present invention. (Thompson et al, 1989, Clin. Chim. Acta 180(3):277-84). Other useful derivatives include, but are not limited to, labels, fluorescent probes such as rhodamine, or FITC, radioactive labels, electroactive labels, affinity tags (e.g., 6His) that can conjugate with secondary labels, oligonucleotides for PCR amplification, such as green fluorescent protein or luciferase, chromogenic peptides, and any combinations thereof.

In one embodiment of the present invention an array of biotinylated lectins of differing carbohydrate specificities is immobilized directly onto wells of streptavidin coated 96-well microtiter plates as illustrated in FIG. 1. Test samples containing different preparations of a given glycosylated enzyme (e.g., aryl sulfatase A (ARSA), agalsidase alfa, galactocerebrosidase (GalC) or heparan N-sulfatase (HNS)) are allowed to bind and unbound material removed by a wash step.

One aspect of the present invention involves the identification and selection of capture agents (e.g., lectins) that demonstrate an affinity for a glycan structure of interest, or for specific glycoforms of a recombinantly prepared enzyme and a determination that such lectins are suitable for binding to the specific enzyme glycoform of interest. The particular capture agent selected for use in the present invention is generally determined based on the ability of such capture agent to bind to a specific glycosylation structure, such as mannose-6-phosphate, fucose, sialic acid, galactose, or any other specific sugar. In some cases, selection of a capture agent is based on the glycosylation of the enzyme targeted for capture. In other cases, the binding agents are selected based on empirical determinations such as high throughput assays. For example, a capture agent can be bound to a solid support and the ability of the capture agent to bind a desired fraction of glycosylated enzyme(s) may be determined by using means known to one of ordinary skill in the art (e.g., an ELISA assay). A capture agent for use in the methods, assays and kits of the present invention may then be selected based upon such capture agent's ability to bind the glycan structure of interest or a particular glycoform of an enzyme in a test sample. A suitable capture agent for use in the present invention may then be used to identify the presence or absence of a glycosylated enzyme of interest in a test sample. For example, such capture agents may be used to determine the presence of a particular glycoform of a recombinant enzyme in a harvest test sample extracted from various stages in the development process of that recombinant enzyme.

A determination of the binding affinity of a particular capture agent for a glycosylated enzyme of interest may be performed by fixing a panel of labeled capture agents (e.g., biotinylated lectins) on a solid support (e.g., a 96 well plate, optionally coated with avidin or streptavidin). The capture agent panel is then contacted with a test sample suspected of containing the glycosylated enzyme of interest. In the presence of the glycosylated enzyme of interest, such enzyme will bind to the capture agent panel and form a bound enzyme complex.

In general, the compositions of the present invention are prepared by attaching (e.g., covalently attaching) at least two (e.g., at least three, at least four, at least five or more) capture agents onto a solid support or to a molecule that is attached to a solid support (e.g., avidin, streptavidin or a nickel chelate). One embodiment of the present invention contemplates the selection of multiple capture agents which are prepared by physically mixing at least two (e.g., three, four, five, or more) distinct capture agents and that are subsequently fixed on one or more solid supports. The amount of a specific capture agent that is selected may be based on the test sample concentration and the approximate concentration of the target glycoenzyme of interest in that test sample. In general, the amount of the capture agent fixed onto a solid support to be contacted by a test sample is in excess of at least about 50% (e.g., at least 75% or at least 100%) of the amount of the portion of the target glycosylated enzyme predicted to bind to the capture agent. Alternatively, capture agents are immobilized on a solid support at various capture agent/solid support ratios or concentrations. The binding capacity of the capture agent/solid support composition may then be determined, or the amount of a test sample that can be loaded without saturating the solid support may be determined. In general, it is desirable that the amount of capture agent fixed on the solid support is at least two-fold in excess of the amount of glycosylated enzyme that is to be bound (e.g., a ten-fold excess or a 100-fold excess).

The invention provides, in part, a capture agent (e.g., multi-capture agent) affinity kit for use in practicing the methods and assays of the invention. The kits of the present invention may include, for example, at least two capture agents (e.g., lectins) bound to one or more solid supports. Examples of such solid supports include, without limitation, one or more beads or microbeads composed of silica, agarose, or a polymer, a plate (e.g., a microtiter plate), a slide (e.g., glass or polymer slide), a nanowell plate, or polyethylene glycol or other soluble polymer that can be precipitated or isolated by some other physical process to which a capture agent is bound. The capture agents used in the invention can be attached to the solid support directly or indirectly (e.g., using an antibody or biotin) using methods known to those of ordinary skill in the art, (e.g., using aldehyde functionalized resins or linkers such as cyanogen bromide, carbonyl diimidazole glutaraldehyde, epoxy, periodate, or bisoxirane) (Harris et al, 1989, In Protein Purification Methods. A Practical Approach, IRL Press, New York, N.Y.). In the case of particulate supports such as agarose beads, a mixture of capture agents (e.g., lectins) may be fixed onto a single bead, or in certain embodiments, a single type of capture agent is attached to each bead and the mixture of capture agents used in the composition is prepared by mixing at least two of these bead populations. Alternatively the capture agent may be attached to a restricted access media for the purposes of selecting glycosylated enzymes of different molecular weight ranges.

The present invention further contemplates the binding of glycosylated enzymes present in a selected test sample, (e.g., recombinant enzymes) to the capture agent to produce a bound enzyme. As used herein, a glycosylated enzyme is said to have “bound” its respective capture agent when it has associated with the capture agent through a non-random chemical or physical interaction. The terms “bind” or “bound” mean the coupling of one molecule (e.g., a glycosylated enzyme, such as the enzymes idursulfase, heparan N-sulfatase, arylsulfatase A, agalsidase alfa and galactocerebrosidase) to another molecule (e.g., a lectin, such as the lectins concanavalin A, sambucus nigra agglutinin and wheat germ agglutinin). Binding of an enzyme to a capture agent is preferably achieved under conditions suitable for such binding to occur. Binding may be achieved by chemical means (e.g., covalent or non-covalent in nature); however in a preferred embodiment, binding of the capture agent to the glycosylated enzyme of interest in the test sample is achieved by way of a covalent bond. Such binding need not be covalent or permanent. Following contact of the capture agent with the test sample, the test sample is preferably contacted with a wash solution such that the excess or unbound test sample fraction can be separated or removed, and if appropriate collected for analysis.

The present invention further contemplates detecting the extent to which a bound enzyme (e.g., the presence of a glycosylated enzyme of interest bound to a capture agent in a selected test sample e.g., recombinant enzymes) competitively inhibits the binding of a ligand to the capture agent bound to the glycosylated enzyme of interest in the test sample. The extent to which a bound enzyme inhibits the binding of a ligand to the capture agent bound to the glycosylated enzyme correlates to the relative amount of glycan associated with the glycosylated enzyme. For example, if the glycosylated enzyme of interest is sialic acid glycosylated idursulfase, and the capture agent is SNA lectin, the extent to which sialic acid glycosylated idursulfase bound to SNA lectin inhibits the binding of a ligand (e.g., agalisidase alfa) to the capture agent, thereby inhibiting the dissociation of idursulfase from SNA lectin, correlates to and thus is indicative of the relative amount of sialic acid content of the glycosylated idursulfase. By way of further example, if the glycosylated enzyme of interest is mannose-6-phosphate glycosylated heparan N-sulfatase, and the capture agent is MP6R, the extent to which mannose-6-phosphate glycosylated heparan N-sulfatase bound to MP6R inhibits the binding of a ligand (e.g., agalsidase alfa) to the capture agent, thereby inhibiting the dissociation of heparan N-sulfatase from MP6R, correlates to and thus is indicative of the relative amount of mannose-6-phosphate content of the glycosylated heparan N-sulfatase. Thus, the extent to which the glycosylated enzyme inhibits the binding of the ligand to the capture agent of the bound enzyme is indicative of the relative amount of glycan associated with the glycosylated enzyme present in the test sample. Generally, the greater the extent to which the bound enzyme inhibits the binding of the ligand to the capture agent, the greater the relative amount of glycan associated with the enzyme in the test sample. Conversely, the lesser the extent to which the bound enzyme inhibits the binding of the ligand to the capture agent, the lesser the relative amount of glycan associated with the enzyme in the test sample. It should be appreciated by those of ordinary skill in the art that any combination of capture agent, ligand, and glycosylated enzyme of interest can be used in the practice of the assays and methods of the present invention as long as the ligand and the glycosylated enzyme of interest have been shown to bind to the selected capture agent in a way that correlates to the relative amount of glycan associated with the particular glycosylated enzyme.

The extent to which the bound enzyme competitively inhibits binding of the ligand to the capture agent is generally performed by contacting the bound enzyme with the ligand. It should be appreciated that any ligand which is a competitive inhibitor which competes with an enzyme suspected of being present in a test sample (e.g., cell harvest sample) for binding to the selected capture agent can be used. In one example embodiment, if the enzyme suspected of being present in the test sample is idursulfase, the competitive inhibitor is agalsidase alfa. In another example embodiment, if the enzyme suspected of being present in the test sample is heparan N-sulfatase, then the competitive inhibitor is agalsidase alfa. In yet another example embodiment, if the enzyme suspected of being present in the test sample is aryl sulfatase A, the competitive inhibitor is agalsidase alfa. Following contact of the bound enzyme with the ligand, the test sample may optionally be contacted with a wash solution such that the excess or unbound test sample fraction (e.g., ligand inhibited from binding to capture agent and glycosylated enzyme dissociated from capture agent) can be separated or removed, and if appropriate collected for analysis.

Generally, the specificity in the detection of the extent to which the bound enzyme inhibits the binding of the ligand to the capture agent will be performed by determining the amount of ligand bound to the capture agent. Determining the amount of ligand bound to the capture agent is performed by detecting the intrinsic enzymatic activity of the ligand bound to the capture agent via addition of appropriate substrate and assay conditions according to the methods of the present invention. The signal determined for a given capture agent (e.g., a lectin) coupled with the known specificity of that capture agent will allow for a fast, high throughput, semi-quantitative structure assessment of the glycoforms present in the test sample. To determine the relative amount of glycan associated with a glycosylated enzyme of interest in a test sample, the bound enzyme fraction (e.g., including both the glycosylated enzyme bound to capture agent and the ligand bound to capture agent) is contacted with a substrate. As used herein, the term “contact” means that two or more substances (e.g., a bound enzyme and a substrate or ligand bound to capture agent and a substrate) are sufficiently close to each other such that the two or more substances interact or react (e.g., chemically or biologically) with one another. The term “substrate” refers to a molecule, complex, material, substance or reactant with which an enzyme reacts (e.g., chemically or biologically), acts or binds. In particular, the substrates of the present invention may demonstrate a physiological, biological and/or chemical affinity for, or be able to be acted upon, by a corresponding enzyme. A substrate useful in the methods of the invention can be native or modified. Modified substrates useful in the invention retain the ability to be acted upon by the corresponding enzyme. Exemplary modifications suitable for substrates include, for example, labeling to confirm the presence or absence of intrinsic enzymatic activity. One aspect of the present invention contemplates the selection of substrates based upon its ability to interact with, or bind to the ligand in a predictable and repeatable fashion. For example, a substrate with which a ligand (e.g., enzyme) is known to react would be preferable. Once a suitable substrate has been identified, that substrate is preferably contacted with the bound enzyme and the ligand bound to the capture agent, and the presence or absence of the anticipated reaction or interaction is assessed.

Based upon the known intrinsic enzymatic activity of the ligand, in the presence of the appropriate substrate the ligand would be expected to react, and accordingly signal the amount of that ligand in the test sample. For example, the product of an enzyme reaction (e.g., a ligand, such as agalsidase alfa, for example) with a substrate (e.g., a molecular entity that is produced or liberated as a result of enzyme acting on substrate) may provide a measurable signal indicative of the presence of ligand in the test sample, and that correlates with the presence or amount of intrinsic enzymatic activity of the ligand in the test sample. Alternatively, quantitative assessments of substrate binding and/or assessments of the conversion of substrate to product may be performed and used as a surrogate marker of intrinsic enzymatic activity of the ligand.

Generally, a greater amount of intrinsic enzymatic activity of the ligand detected is indicative of a lesser extent to which the bound enzyme inhibits the binding of the ligand to the capture agent, and a lesser amount of intrinsic enzymatic activity detected is indicative of a greater extent to which the bound enzyme inhibits the binding of the ligand to the capture agent. Said differently, a greater amount of intrinsic enzymatic activity of the ligand bound to the capture agent detected is indicative of a lesser relative amount of glycan associated with the glycosylated enzyme of interest in the test sample, and a lesser amount of intrinsic enzymatic activity of the ligand bound to the capture agent is indicative of a greater relative amount of glycan associated with the glycosylated enzyme of interest in the test sample.

Examples of suitable substrates for use in the present invention include 4-nitrophenyl-α-D-galactopyranoside, 4-nitrophenyl-β-D-galactopyranoside and para-nitrocatechol sulfate.

Selection of the appropriate enzyme (e.g., ligand) substrate and the subsequent determination of intrinsic enzymatic activity of the enzyme require an understanding of enzyme kinetics and in particular the catalytic properties of the enzyme(s) being evaluated. For example, enzymatic properties, such as Michaelis-Menton constants (K_(m)) and/or turnover numbers (K_(cat)) relating to a particular substrate provide the basis for evaluating the sensitivity of an enzyme for one or more substrates and provide information regarding the reproducibility of the methods, kits and assays contemplated by the present inventions.

As used herein, the term “intrinsic enzymatic activity” refers to the repeatable reaction which an enzyme (e.g., ligand) catalyzes or causes to occur, for example in the presence of a substrate with which such enzyme is known to react. In one embodiment of the present invention, the intrinsic enzymatic activity of ligand may be exploited to confirm the presence or absence of such ligand in a particular test sample. For example, many enzymes have known and repeatable catalytic activity, which may be enhanced under certain conditions, such as the presence of the appropriate substrate. Intrinsic enzymatic activity may be measured by routine means known to one of ordinary skill in the art (e.g., colorimetric, spectrophotometric, fluorometric or chromatographic assays) by determining, for example the production of a product over time. In accordance with the present invention, following contacting a ligand with a substrate, a relative increase in the formation of a product, or the conversion of that substrate to product, in each case of about 5%, 10%, 20%, 30%, 40%, 50% or more, or preferably about 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 99%, or more preferably 100% or more, may be indicative of intrinsic enzymatic activity of the ligand.

The methods described herein are useful for development of kits that can be used for the detection of enzymes and the relative amount of glycan associated with the enzymes in a test sample. Such kits include one or more capture agents (e.g., lectins or fusion proteins) fixed on a solid support which are capable of binding to a glycosylated enzyme present in a selected test sample. The kits may also include additional reagents such as buffers, substrates, enzymes, chemicals and other compositions useful for further analysis and/or quantification of the ligand-bound capture agent fraction. Kits can also include components for test sample preparation. The methods and kits described herein are useful for providing a platform for the semi-quantitative assessment of the presence of glycosylated enzymes and the relative amount of glycan associated with the glycosylated enzyme in a test sample.

While certain compounds, compositions and methods of the present invention have been described with specificity in accordance with certain embodiments, the following examples serve only to illustrate the methods, assays, kits and compositions of the invention and are not intended to limit the same.

The articles “a” and “an” as used herein in the specification and in the claims, unless clearly indicated to the contrary, should be understood to include the plural referents. Claims or descriptions that include “or” between one or more members of a group are considered satisfied if one, more than one, or all of the group members are present in, employed in, or otherwise relevant to a given product or process unless indicated to the contrary or otherwise evident from the context. The invention includes embodiments in which exactly one member of the group is present in, employed in, or otherwise relevant to a given product or process. The invention also includes embodiments in which more than one, or the entire group members are present in, employed in, or otherwise relevant to a given product or process. Furthermore, it is to be understood that the invention encompasses all variations, combinations, and permutations in which one or more limitations, elements, clauses, descriptive terms, etc., from one or more of the listed claims is introduced into another claim dependent on the same base claim (or, as relevant, any other claim) unless otherwise indicated or unless it would be evident to one of ordinary skill in the art that a contradiction or inconsistency would arise. Where elements are presented as lists, (e.g., in Markush group or similar format) it is to be understood that each subgroup of the elements is also disclosed, and any element(s) can be removed from the group. It should be understood that, in general, where the invention, or aspects of the invention, is/are referred to as comprising particular elements, features, etc., certain embodiments of the invention or aspects of the invention consist, or consist essentially of, such elements, features, etc. For purposes of simplicity those embodiments have not in every case been specifically set forth in so many words herein. It should also be understood that any embodiment or aspect of the invention can be explicitly excluded from the claims, regardless of whether the specific exclusion is recited in the specification. The publications and other reference materials referenced herein to describe the background of the invention and to provide additional detail regarding its practice are hereby incorporated by reference.

Example 1

Studies performed using the inventions disclosed herein have demonstrated carbohydrate-specific binding of agalsidase alfa and galactocerebrosidase drug substance material to several capture agents. The capture agents evaluated included the biotinylated lectins ConA (specific for core α-mannose structures), WGA (specific for dimers and trimers of N-acetyl-glucosamine), and SNA (specific for Neu5Ac(α2,6)Gal structures).

Technical Feasibility

To determine the technical feasibility of the methods, assays and compositions described herein, purified agalsidase alfa, aryl sulfatase A and galactocerebrosidase samples were initially assessed. The choice of capture agent was initially limited to only a select few lectins with well defined binding specificities. The lectin capture agents utilized included: (1) concanavalin A (Con A), one of the most commonly used lectins and known to bind avidly to core α-mannose structures of N-linked high-mannose and biantennary complex-type oligosaccharides, (2) Sambucus nigra lectin (SNA) and Maackia amurensis lectin (MAL), which recognize Neu5Ac(α2, 6)Gal and Neu5Ac(α2, 3)Gal respectively, (3) Ricinus communis agglutinin I (RCAI), which binds terminal β1,4-linked Gal, and (4) wheat germ agglutinin (WGA), which binds poly-lactosamine repeats Galβ1,4GlcNAc. Technical feasibility was based on sensitivity of detection. Feasibility was further evaluated using in-process test samples provided from cell culture/process development streams.

Results

Method feasibility was evaluated using agalsidase alfa (Replagal®) drug substance and the biotinylated lectins ConA and WGA as the capture agents. The binding of decreasing agalsidase alfa concentrations (40 ug/mL to 300 ng/mL) to the immobilized lectins was analyzed by measuring the enzymatic activity of the bound enzyme. The enzyme activity of agalsidase alfa was determined under steady-state conditions for the synthetic colorimetric substrate 4-nitrophenyl-α-D-galactopyranoside. The substrate was hydrolyzed into 4-nitrophenol and α-D-galactopyranoside where the p-nitrophenol product was read at 405 nm once the reaction was halted with an alkaline buffer. The binding curves of agalsidase alfa (Replagal®) by both WGA and ConA (in absorbance units) are shown in FIG. 2.

The high avidity for ConA (which is specific for α-linked mannose structures) at all concentrations tested demonstrated the high sensitivity of the assays and methods described herein. The binding for WGA (which is specific for dimers and trimers of N-acetyl-glucosamine) was less avid and followed a more classical titration curve. These studies demonstrated the potential of the methods and assays of the present invention in terms of their sensitivity and high-throughput nature.

Example 2

Method feasibility was further evaluated with galactocerebrosidase (GalC) drug substance material and the biotinylated lectins concanavalin A (Con A), wheat germ agglutinin (WGA), and Sambucus nigra lectin (SNA). The binding curves in FIG. 3 demonstrate both strong and selective binding to GalC.

To determine whether the methods and assays of the present invention were capable of detecting differences in the amount of GalC-associated sialic acid, GalC samples were subjected to increasing amounts of sialidase pre-treatment and then evaluated for binding. The results provided in FIG. 4 demonstrate that controlled removal of sialic acid results in reduced binding, providing evidence that the assays and methods of the present invention are capable of measuring differences in the amount of GalC-associated sialic acid.

Example 3

To confirm the sialic acid binding specificity of Sambucus nigra lectin (SNA), aryl sulfatase A drug substance samples produced in CHO and human cells containing approximately 1 mol of sialic acid per mol of protein in either α2,6-linkage (human cell-derived) or α2,3-linkage (CHO cell-derived) were analyzed for binding.

The binding curves provided in FIG. 5 illustrate both the selective binding for sialic acid in the α2,6-linkage and the α2,3-linkage.

Example 4

To determine whether the assays, methods and compositions described herein could be applied to actual harvest samples, early, middle, and late galactocerebrosidase (GalC) harvest samples (H2, H10, and H17) from an early stage in the development process were analyzed for binding to Sambucus nigra lectin (SNA).

The results shown in FIG. 6 demonstrate no difference in sialic acid binding across all 3 harvests and importantly validate the intended purpose of the present invention.

Example 5

The feasibility of the present invention was also evaluated with aryl sulfatase A drug substance material derived from two different production methods and a recombinant fusion protein which was prepared to function as the capture agent. The recombinant fusion protein consisted of the high affinity binding domain (D9) of the mannose-6-phosphate receptor (M6PR) linked to six histidine residues (6His) to facilitate fixation of the M6PR to a nickel chelate coated solid support. The recombinant fusion protein construct is referred to herein as M6PR(D9)6His and was expressed in HT1080 cells, purified using nickel chelate affinity chromatography, and was affixed onto a 96-well plate.

To determine whether the methods and assays of the present invention were capable of detecting differences in the amount of aryl sulfatase A associated M6P associated with the two different production methods, aryl sulfatase A lots with known amounts of M6P were evaluated for binding to immobilized M6PR(D9)6His (FIG. 7). Increasing concentrations of test samples designated as either HGT-1110 or HGT-1111 (corresponding to the respective production methods) were added to the wells and allowed to bind for 2 hours at room temperature. The wells were washed in PBS and the enzyme activity was measured using the substrate p-nitrocatechol sulfate.

As shown in FIG. 8, aryl sulfatase A from lot HGT-1111 which known to include more that 2×M6P per mol of protein as compared to aryl sulfatase A from HGT-1111, displayed more avid binding as compared to aryl sulfatase A from lot HGT-1110. These results demonstrate that the methods, assays and kits of the present invention are capable of measuring differences in the amount of aryl sulfatase A-associated M6P.

Example 6

Agalsidase alfa has been demonstrated to bind to Sambucus nigra lectin (SNA) in a manner that correlates to the amount of sialic acid associated with agalsidase alfa. The feasibility of the present invention was also evaluated with idursulfase, heparan N-sulfatase (FINS), and aryl sulfatase A (ARSA) drug substance materials as competitive inhibitors of the binding of the ligand agalsidase alfa to the capture agent Sambucus nigra lectin.

To determine whether the methods and assays of the present invention were capable of detecting differences in the relative amounts of sialic acid associated with idursulfase, heparan N-sulfatase, and aryl sulfatase, agalsidase alfa lots with known amounts of sialic acid were evaluated for binding to SNA immobilized in 96-well plates in the presence of increasing concentrations of idursulfase (◯), FINS (□), or ARSA (▴) (FIG. 9). The amount of agalsidase alfa bound, and the half maximal inhibitory concentrations (IC₅₀) of each drug substance, was determined by measuring the intrinsic enzymatic activity of agalsidase alfa bound to SNA in accordance with the methods of the present invention.

As shown in Table 1 below, idursulfase was the most potent inhibitor of sialic acid binding with an IC₅₀ of 2.3×10⁻⁸ M, followed by FINS with an IC₅₀ of 2.2×10⁻⁷ M and then ARSA with IC₅₀ 1.2×10⁻⁶ M. Note that these results are consistent with the relative amounts of sialic acid associated with idursulfase, FINS, and ARSA, respectively. These results demonstrate that the methods, assays and kits of the present invention are capable of detecting the relative amounts of glycan (e.g., sialic acid) associated with a glycosylated enzyme (e.g., such as idursulfase, HNS, and ARSA, for example) in a way that correlates to the extent to which the glycosylated enzyme competitively inhibits the binding of a ligand (e.g., agalsidase alfa) to a capture agent (e.g., SNA lectin).

TABLE 1 Half maximal inhibitory concentrations (IC₅₀) of glycosylated enzyme inhibiting binding of agalisidase alfa to SNA lectin Glycosylated Enzyme IC₅₀ (nM) Idursulfase 23 HNS 215 ARSA 1209

Example 7

Agalsidase alfa has been demonstrated to bind to MP6 Receptor (MP6R) in a manner that correlates to the amount of mannose-6-phosphate associated with agalsidase alfa. The feasibility of the present invention was also evaluated with idursulfase, heparan N-sulfatase (HNS), and aryl sulfatase A (ARSA) drug substance materials as competitive inhibitors of the binding of the ligand agalsidase alfa to the capture agent MP6R.

To determine whether the methods and assays of the present invention were capable of detecting differences in the relative amounts of mannose-6-phosphate associated with idursulfase, heparan N-sulfatase, and aryl sulfatase, agalsidase alfa lots with known amounts of mannose-6-phosphate were evaluated for binding to MP6R immobilized in 96-well plates in the presence of increasing concentrations of idursulfase (◯), HNS (□), or ARSA (▴) (FIG. 10). The amount of agalsidase alfa bound, and the half maximal inhibitory concentrations (IC₅₀) of each drug substance, was determined by measuring the intrinsic enzymatic activity of agalsidase alfa bound to MP6R in accordance with the methods of the present invention.

As shown in Table 2 below, idursulfase was the most potent inhibitor of mannose-6-phosphate binding with an IC₅₀ of 1.3×10⁻⁸ M, followed by HNS with an IC₅₀ of 3.6×10⁻⁸ M and then ARSA with an IC₅₀ 1.9×10⁻⁷ M. Note that these results are consistent with the relative amounts of mannose-6-phosphate associated with idursulfase, HNS, and ARSA, respectively. These results demonstrate that the methods, assays and kits of the present invention are capable of detecting the relative amounts of glycan (e.g., mannose-6-phosphate) associated with a glycosylated enzyme (e.g., such as idursulfase, HNS, and ARSA, for example) in a way that correlates to the extent to which the glycosylated enzyme competitively inhibits the binding of a ligand (e.g., agalsidase alfa) to a capture agent (e.g., MP6R).

TABLE 2 Half maximal inhibitory concentrations (IC₅₀) of glycosylated enzyme inhibiting binding of agalisidase alfa to MP6R Glycosylated Enzyme IC₅₀ (nM) Idursulfase 13 HNS 36 ARSA 189 

What is claimed is:
 1. A method for detecting the presence of an enzyme and/or the relative amount of glycan associated with said enzyme in a test sample, wherein said method comprises the steps of: (a) contacting said test sample with at least one capture agent under conditions appropriate for binding of glycosylated enzyme in said test sample to said capture agent, wherein if said glycosylated enzyme is present in said test sample a bound enzyme is formed; (b) separating said bound enzyme from said test sample; and (c) detecting the extent to which said bound enzyme inhibits binding of a ligand to said capture agent, wherein the extent to which said bound enzyme inhibits binding of said ligand to said capture agent is indicative of the relative amount of glycan associated with said enzyme in said test sample; wherein said capture agent comprises a fusion protein, and wherein said fusion protein comprises at least one M6PR binding domain. 2-4. (canceled)
 5. The method of claim 1, wherein said fusion protein comprises M6PR binding domain
 9. 6. The method of claim 1, wherein said fusion protein comprises six consecutive histidine residues (6His). 7-11. (canceled)
 12. The method of claim 1, wherein the step of detecting the extent to which said bound enzyme inhibits binding of said ligand to said capture agent is performed by contacting said bound enzyme with said ligand.
 13. The method of claim 12, wherein said ligand is a competitive inhibitor which competes with an enzyme suspected of being present in said test sample for binding to said capture agent.
 14. The method of claim 13, wherein said enzyme is idursulfase and said competitive inhibitor is agalsidase alfa.
 15. The method of claim 13, wherein said enzyme is heparan N-sulfatase and said competitive inhibitor is agalsidase alfa.
 16. The method of claim 13, wherein said enzyme is aryl sulfatase A and said competitive inhibitor is agalsidase alfa.
 17. The method of claim 1, wherein the greater the extent to which said bound enzyme inhibits binding of said ligand to said capture agent is indicative of a greater relative amount of glycan associated with said enzyme in said test sample, and wherein the lesser the extent to which said bound enzyme inhibits binding of said ligand to said capture agent is indicative of a lesser relative amount of glycan associated with said enzyme in said test sample.
 18. The method of claim 12, wherein the step of detecting the extent to which said bound enzyme inhibits binding of said ligand to said capture agent comprises determining the amount of said ligand bound to said capture agent.
 19. The method of claim 18, wherein the step of determining the amount of said ligand bound to said capture agent comprises detecting the intrinsic enzymatic activity of said ligand bound to said capture agent.
 20. The method of claim 19, wherein the step of detecting intrinsic enzymatic activity of said ligand bound to said capture agent is performed by contacting said ligand bound to said capture agent with a substrate.
 21. The method of claim 20, wherein said substrate is reactive with said ligand bound to said capture agent.
 22. The method of claim 20, wherein the conversion of said substrate to product is indicative of intrinsic enzymatic activity.
 23. The method of claim 19, wherein the step of detecting intrinsic enzymatic activity comprises quantitatively determining the presence of a product formed after contacting said ligand bound to said capture agent with said substrate,
 24. The method of claim 23, wherein the presence of said product is indicative of intrinsic enzymatic activity.
 25. The method of claim 20, wherein said ligand is agalsidase alfa and said substrate is 4-nitrophenyl-α-D-galactopyranoside.
 26. The method of claim 1, wherein said enzyme is idursulfase and said glycan is sialic acid.
 27. The method of claim 1, wherein said enzyme is idursulfase and said glycan is mannose-6-phosphate.
 28. The method of claim 1, wherein said enzyme is heparan N-sulfatase and said glycan is sialic acid.
 29. The method of claim 1, wherein said enzyme is heparan N-sulfatase and said glycan is mannose-6-phosphate.
 30. The method of claim 1, wherein said enzyme is aryl sulfatase A and said glycan is sialic acid.
 31. The method of claim 1, wherein said enzyme is aryl sulfatase A and said glycan is mannose-6-phosphate.
 32. (canceled)
 33. The method of claim 1, wherein the step of separating said bound enzyme from said test sample is performed by washing.
 34. A method for detecting the presence of an enzyme and the relative amount of glycan associated with said enzyme in a test sample, wherein said method comprises the steps of: (a) contacting a test sample with at least one capture agent under conditions appropriate for binding of glycosylated enzyme, wherein if said glycosylated enzyme is present in said test sample a bound enzyme is formed; (b) separating said bound enzyme from said test sample; (c) contacting said bound enzyme with at least one ligand for said capture agent; and (d) detecting the extent to which said bound enzyme inhibits binding of said ligand to said capture agent, wherein the extent to which said bound enzyme inhibits binding of said ligand to said capture agent is indicative of the relative amount of glycan associated with said enzyme in said test sample; wherein said capture agent comprises is a fusion protein, and wherein said fusion protein comprises at least one M6PR binding domain. 35-37. (canceled)
 38. The method of claim 34, wherein said fusion protein comprises M6PR binding domain
 9. 39. The method of claim 34, wherein said fusion protein comprises six consecutive histidine residues (6His).
 40. The method of claim 34, wherein said ligand is a competitive inhibitor which competes with an enzyme suspected of being present in the test sample for binding to said capture agent.
 41. The method of claim 40, wherein said enzyme is idursulfase and said competitive inhibitor is agalsidase alfa.
 42. The method of claim 40, wherein said enzyme is heparan N-sulfatase and said competitive inhibitor is agalsidase alfa.
 43. The method of claim 40, wherein said enzyme is aryl sulfatase A and said competitive inhibitor is agalsidase alfa.
 44. The method of claim 34, wherein the greater the extent to which said bound enzyme inhibits binding of said ligand to said capture agent is indicative of a greater relative amount of said glycan associated with said enzyme glycoform in said test sample, and wherein the lesser the extent to which said bound enzyme inhibits binding of said ligand to said capture agent is indicative of a lesser relative amount of glycan associated with said enzyme glycoform in said test sample.
 45. The method of claim 34, wherein the step of detecting the extent to which said bound enzyme inhibits binding of said ligand to said capture agent comprises determining the amount of said ligand bound to said capture agent.
 46. The method of claim 45, wherein the step of determining the amount of said ligand bound to said capture agent comprises detecting the intrinsic enzymatic activity of said ligand bound to said capture agent.
 47. The method of claim 46, wherein the step of detecting intrinsic enzymatic activity of said ligand bound to said capture agent is performed by contacting said ligand bound to said capture agent with a substrate.
 48. The method of claim 47, wherein said substrate is reactive with said ligand bound to said capture agent.
 49. The method of claim 47, wherein the conversion of said substrate to product is indicative of intrinsic enzymatic activity.
 50. The method of claim 46, wherein the step of detecting intrinsic enzymatic activity comprises quantitatively determining the presence of a product formed after contacting said ligand bound to said capture agent with said substrate.
 51. The method of claim 50, wherein the presence of said product is indicative of intrinsic enzymatic activity.
 52. The method of claim 47, wherein said ligand is agalsidase alfa and said substrate is 4-nitrophenyl-α-D-galactopyranoside.
 53. The method of claim 34, wherein said enzyme is idursulfase and said glycan is sialic acid.
 54. The method of claim 34, wherein said enzyme is idursulfase and said glycan is mannose-6-phosphate.
 55. The method of claim 34, wherein said enzyme is heparan N-sulfatase and said glycan is sialic acid.
 56. The method of claim 34, wherein said enzyme is heparan N-sulfatase and said glycan is mannose-6-phosphate.
 57. The method of claim 34, wherein said enzyme is aryl sulfatase A and said glycan is sialic acid.
 58. The method of claim 34, wherein said enzyme is aryl sulfatase A and said glycan is mannose-6-phosphate. 59-63. (canceled)
 64. The method of claim 34, wherein said bound enzyme is separated from said test sample by washing.
 65. A kit for detecting the presence of glycosylated enzyme and the relative amount of glycan associated with said glycosylated enzyme in a test sample, wherein said kit comprises (a) at least one capture agent, wherein said capture agent is capable of binding said glycosylated enzyme, and (b) at least one ligand, wherein said ligand is competitive with said glycosylated enzyme for binding said at least one capture agent; wherein said capture agent is a fusion protein, and wherein said fusion protein comprises at least one M6PR binding domain. 66-68. (canceled)
 69. The kit of claim 65, wherein said fusion protein comprises M6PR binding domain
 9. 70. The kit of claim 65, wherein said fusion protein comprises six consecutive histidine residues (6His).
 71. The kit of claim 65, wherein said kit further comprises a solid support.
 72. The kit of claim 71, wherein said capture agent is affixed onto said solid support. 73-76. (canceled)
 77. The kit of claim 65, wherein said glycosylated enzyme is selected from the group consisting of idursulfase, heparan N-sulfatase, and aryl sulfatase A.
 78. (canceled)
 79. The kit of claim 65, wherein said ligand is agalsidase alfa.
 80. The kit of claim 65, wherein said ligand is agalsidase alfa, and said glycosylated enzyme is selected from the group consisting of idursulfase, heparan N-sulfatase, and aryl sulfatase A.
 81. The kit of claim 65, further comprising a substrate.
 82. The kit of claim 81, wherein said substrate is 4-nitrophenyl-β-D-galactopyranoside.
 83. The kit of claim 65, wherein said kit further comprises a means to separate said bound enzyme from said test sample. 